The plasmalemma forming microappendages on the ventral surface of the 18-24 hour chick embryo will be examined by freeze-fracturing techniques, with special attention given to concentrations of particulate material within the lipoprotein membrane. Efforts will be made to correlate these data with the pleomorphism of the microappendages as demonstrated by SEM. The effects of numerous other substances known to alter lipoprotein membranes will be tested on the microappendages of the early chick embryo.